The present invention relates to food wrappings, and more particularly, to non-edible casings for meat and sausage products. They are formed of a fibrous reinforcement impregnated with a continuous cross-linked matrix of an amylose-containing material to provide a composite type wrapping characterized by high wet strength with little or virtually no age embrittlement, and therefore, are especially useful for stuffing larger size meat products, such as braunschweiger, bologna, salami, hams and the like.
Amylose polymers have been used heretofore in food wrapping applications. However, use of amylose in food casings has been restricted to non-reinforced edible types having very low wet strengths, as for example, those used in packaging fresh link sausages where tenderness of the film is considered a desirable property to impart appropriate bite to the casing which is ingested with the meat product. Many of these fragile, edible type amylose casings are prestuck or perforated with holes to provide for egress of fats and oils from the meat when cooked by the consumer. One such example is described in U.S. Pat. No. 4,226,264 where high elasticity is imparted to edible sausage casings by a helical pattern of cross-linked amylose units assuring encased meat products with tightly drawn casings even with shrinkage of the meat as a result of the cooking process. In spite of their favorable properties however, prior art unreinforced amylose casings, such as those of U.S. Pat. No. 4,226,264 have wet strengths resistant to break forces typically well below 1000 psi, and therefore, lack the strength and toughness needed for stuffing larger, heavier meat products like hams, bolognas, etc.
Other digestible starch and amylose casings are described in U.S. Pat. No. 2,729,565 where frankfurters are prepared in casings formed from substantially pure amylose, or alternatively, a major proportion of amylose and a minor proportion of amylopectin. Although U.S. Pat. No. 2,729,565 suggests molecular orientation of the film for increased strength, the casings nevertheless, lack the required wet strength and toughness for stuffing large size meat products. Accordingly, the present invention relates to novel reinforced amylose and high amylose content starch food wrappings, including casings having sufficient wet strength and toughness to resist the break force normally associated with packaging large size meat products.
As previously indicated, amylose-containing polymers have had only limited application as food casings, mainly because of exceedingly low wet strengths. But in addition, amylose was not widely used as a result of its glass-like brittleness and poor elongation properties, particularly with the evaporation of moisture from the film. Even at 50 percent relative humidity amylose films have a low percent elongation and can become brittle as to render them, as a practical matter, useless as food casings. As a result, food grade polyols, like glycerin, customarily used to plasticize brittle polymers, such as in cellulose casings, have been suggested for plasticizing amylose films. However, U.S. Pat. Nos. 3,312,560 and 3,318,715 which teach amylose films laminated or coated to cellulose bases, e.g. cellophane, paper, to impart special properties thereto confirm that at low relative humidities prior art amylose films plasticized with glycerin have about the same elastic modulus and percent elongation as unplasticized amylose films. In fact, nonreinforced, non-cross-linked amylose films become embrittled usually within three to five weeks even when plasticized with glycerin.
Accordingly, a further aspect of the present invention lies in the discovery that aging embrittlement of plasticized amylose films and casings can be minimized or virtually eliminated by fibrous reinforcement and through cross-linking. Unexpectedly, it was found that fibrous reinforced, cross-linked amylomaceous composite casings of the present invention plasticized with food grade polyols, such as glycerin, do not undergo embrittlement with age. This provides important advantages, including storageability of the wrappings and casings before use without consequential losses in wet strength and elongation at break.
A high percentage of the non-edible cellulose type food casings widely used are manufactured by the well-known viscose process. The process typically provides for chemically regenerating a web saturated with sodium cellulose xanthate, including by-products of xanthation dissolved in caustic soda. In the process of regenerating the cellulose, carbon disulfide and hydrogen sulfide are produced as by-products. As a result, cellulose casings must be manufactured under stringent standards to protect the health of workers in production areas from exposure to unsafe levels of these potentially harmful byproducts. Similarly, plant effluents must be treated, for example, with scrubbers before being discharged into the environment. Accordingly, the present invention provides a practical alternative for the widely used fibrous reinforced cellulose type casings which not only offers a more economical alternative in terms of raw materials and production costs, but also a product that can be manufactured by a novel method which causes fewer environmental problems.